1. Field of the Invention
The present invention relates to a system for estimating a fault mode in a semiconductor device such as a CMOS integrated device.
2. Description of the Related Art
In a first prior art system for detecting a failure mode in a semiconductor device, an electron beam is incident to the device, and as a result, a potential map or the like is obtained by detecting secondary electrons generated from the device. Then, a fault mode is detected by observing the device with an optical microscope, by etching the device with a laser beam or by cutting the device with a focused ion beam (FIB).
In the first prior art system, however, since determination of a fault mode is carried out by using physical analysis, it takes a lot of time to completely determine a fault mode.
A second prior art system for detecting a failure mode in a semiconductor device uses an optical emission microscope having a function for accumulating detected light (sees H. Ishizuka at al., "STUDY OF FAILURE ANALYSIS USING PHOTON SPECTRUM", REAJ 4-TH SYMPOSIUM, VoL. 13, No. 3, pp.71-76, November 1991). This will be explained later in detail.
In the second prior art system, however, detected failure modes are limited to an open failure mode of a gate electrode, a leakage failure mode by the destruction of a gate oxide layer, and a short-circuit node between connections by a high resistance conductor, for example. Also, it is impossible to accurately estimate a failure mode, since the emission spectrum of one failure mode is similar to the emission spectrum of another failure mode. Further, it is necessary to specify a fault point before the analysis by the optical emssion mictroscope. Further, if a fault point is beneath a conductive layer, it is impossible to detect light generated from such a fault point, since the light is reflected by the conductive layer. In addition, when a leakage current flowing through a fault point is so large as to remarkably increase the light intensity, it is impossible to normally operate the optical emission microscope.
In a third prior art system for detecting a failure mode in a semiconductor device, a signal waveform is obtained by an electron beam or a laser beam or by a direct probing using a metal needle, and is compared with a simulated waveform. As a result, if the signal waveform is different from the simulated waveform, a logic simulation is carried out to determine a fault mods.
In the third prior art system, however, it takes a lot of time to determine a fault mode, since a large amount of time is required to analyze the result of the logic simulation.